Display screens are widely used for computer monitors, televisions and many other consumer and commercial display applications. Some flat panel display screens include an array of optical shutters and a backlight system that impinges light on the display screen.
For example, LCD devices are widely used in flat panel displays for monitors, televisions and other consumer and commercial display applications. As is well known to those having skill in the art, an LCD display generally includes an array of LCD devices that act as an array of optical shutters. Transmissive LCD displays employ backlighting using, for example, fluorescent cold cathode tubes above, beside and sometimes behind the array of LCD devices. A diffusion panel behind the LCD devices can be used to redirect and scatter the light evenly to provide a more uniform display.
Conventional shuttered display devices generally include three different color picture elements (often referred to as pixels and/or subpixels), generally red (R), green (G) and blue (B) picture elements. A backlight system for shuttered display devices may be configured to uniformly radiate light on the display screen that provides the appearance of white light. As used herein, “different colors” means different frequency spectra having different center frequencies.
It is also known to provide an array of fluorescent cold cathode tubes behind and facing the planar array of LCD devices. Unfortunately, an array of fluorescent cold cathode tubes may increase the thickness of the LCD display and/or increase the power consumption thereof. It also may be difficult to uniformly illuminate the planar array of LCD devices with the array of fluorescent cold cathode tubes.
Semiconductor light emitting devices, such as Light Emitting Diode (LED) devices, also may be used for edge illumination of a planar array of LCD devices. For example, U.S. patent application Ser. No. 10/898,608, filed Jul. 23, 2004, entitled Reflective Optical Elements for Semiconductor Light Emitting Devices, to the present inventor Negley, and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes side emission LEDs that may be used for large area LCD and/or television backlighting.
LED devices also may be used for direct backlighting of LCD displays. For example, U.S. patent application Ser. No. 11/022,332, filed Dec. 23, 2004, entitled Light Emitting Diode Arrays For Direct Backlighting Of Liquid Crystal Displays, to the present inventor Negley, and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes a display panel for a flat panel display that includes a planar array of LCD devices and a planar array of LED devices that is closely spaced apart from the planar array of LCD devices, to provide backlighting for the planar array of LCD devices.
As is well known to those having skill in the art, the electrical and/or optical parameters of individual LED devices that are fabricated may vary considerably, for example, due to routine process variations. In order to provide backlighting uniformity and/or to provide a desired backlighting color point, it may be desirable to sort or “bin” LED devices that are to be used for backlighting applications, to allow close matching of electrical and/or optical parameters of the LED devices. Unfortunately, this binning may produce additional manufacturing complexity and/or may lead to at least some of the LED devices being rejected as being unsuitable. Binning and/or rejection of some LED devices also may increase the resultant cost of LED backlighting systems.